Purge more bloat from registry.json

[HebaruSan]

Motivation

The registry.json file nowadays is about 20 MB, 10% of which is repetitions of the following lines:

Line	Occurrences
"ksp_version_strict": false,	14817
"download_content_type": "application/zip",	14764
"find_matches_files": false,	13504
"install_to": "GameData" (without a comma)	8378
"install_to": "GameData", (with a comma)	1725

A further 3.5 MB is tab characters indenting the JSON. While it can be useful to inspect this file from time to time, its primary function is to be read by code, so this formatting is not necessary.

This takes up disk space and increases the time to save and load the registry.

Changes

Now the above values of the above properties are treated as the default; when the property has that value, it will be left out of the serialization, and if the property is missing when de-serializing, it will be set to the default. There will be no change in runtime behavior because the de-serializer will still set the properties as needed.

Similarly, the indenting is removed (but the line breaks remain).

This reduces the size of registry.json by about 5.5 MB, similar to #2179.

-rw-r--r-- 1 20846338 Nov  2 18:42  OLD-registry.json
-rw-r--r-- 1 15320905 Nov  2 19:02  NEW-registry.json

$ echo $((20846338-15320905))
5525433

[Olympic1]

We can save another 5MB if we remove the indentation of the json.

Downside is that it will be very hard to read as everything is set on 1 line.

Code that indents the json:

CKAN/Core/Registry/RegistryManager.cs

Lines 361 to 363 in caeb50d

	writer.Formatting = Formatting.Indented;
	writer.Indentation = 1;
	writer.IndentChar = '\t';

[HebaruSan]

Hmm, it's not too bad if we keep the line breaks:

[Olympic1]

Doesn't look bad. We can always remove the identation completely if the file grows too big again.